The startup pop elimination system can be a central element of an audio power conversion system.
Most audio power converters are based on a PWM (Pulse Width Modulation) modulator (digital modulator or analogue modulator) that converts a PCM (Pulse Code Modulated) signal received from a source such as a CD-player, or an analogue signal preceded by a D/A (Digital to Analogue) converter, to for instance pulse-width-modulated signals (digital or analogue PWM modulator).
The output signal of the modulator is fed to a power stage where it is amplified. A typical power converter includes a switching power conversion stage, a filter and an analogue control system.
At start-up of the audio power conversion system a general problem is the presence of an audible signal at the output of the system even though there is no input signal applied to the audio power conversion system. The signal at the output at start-up is called pop.
A contributing source of the start-up pop can be transients when the control system is started from a saturated position.
When the amplifier starts up the control system will find its correct bias value. It is therefore desired that the control system is correctly biased before startup.
In WO 2008/072212 the close down pop is minimized by including a parallel power stage with a switch in serial at the output. This implementation is complex since one more power stage is needed.
U.S. Pat. No. 6,538,590 describes a system using a serial resistor for ramping up. Not for a system with a control loop.
US 2007/0139103 describes a system for quiet power up and power down of an audio amplifier, however it is only applicable in digital systems.
There is therefore a need for an improved system and method for minimizing the start-up pop often present in audio power conversion systems.